Method of Transferring Particles

ABSTRACT

Method and apparatus are provided for transferring particles from an upper zone through an intermediate zone to a lower zone. The transfer of particles between the zones through valveless conduits is regulated by varying the pressure of the intermediate zone and the flow rate of gas passing through the valveless conduits. A container within the second zone is in particle communication with a valveless conduit and provides more consistent particle flows.

FIELD OF THE INVENTION

This invention generally relates to the art of solid particle transport.More specifically, the invention relates to methods and apparatus fortransferring particles from an upper zone through a middle zone to acontainer within a lower zone.

BACKGROUND OF THE INVENTION

There are many chemical processes where it is necessary to bring intocontact a fluid and a solid particulate matter, such as adsorbents andcatalysts. Frequently, chemical reactions as well as physical phenomenaoccur for a predetermined period of time in the contact zone, e.g. areaction or adsorption zone. In many of these processes, the particlesare transported between two or more particle containing vessels. Theparticles may be transported for a variety of reasons depending on theprocess. For example, particles may be transported from one contactingvessel or zone into another contacting zone in order to take advantageof different process conditions to improve product yields and/or purity.In another example, particles may be transported from a reaction zoneinto a regeneration zone in order to rejuvenate the particles, and afterrejuvenation, the particles may be transported back to the reactionzone. The particles may be introduced to and withdrawn from the vesselsor zones in a continuous or semi-continuous manner sufficient tomaintain the desired contacting process continuously.

The vessels between which the catalyst is transported are notnecessarily adjacent. The outlet of the source vessel from which thecatalyst is transported may be a significant distance horizontallyand/or vertically from the inlet of the destination vessel to which thecatalyst is transported. Pneumatic conveying through a conduit is a wellknown and commonly used method of transferring catalyst over verticaland horizontal distances. One characteristic of pneumatic conveying isthat because of the pressure difference across the conduit between thesource and destination, the destination pressure must be less than thesource pressure to account for the pressure drop across the pneumaticconveying system. However, process conditions may require thedestination vessel to operate at a higher pressure than this value(source pressure minus pneumatic conveying system pressure drop).Examples include circulating particles between two zones maintained atdifferent pressures; and transferring particles from one vessel toanother where both vessels are maintained at the same pressure. Undersuch conditions, a pneumatic conveying system alone is insufficient totransfer the particles.

A lock hopper is commonly used to transfer particles from a lowerpressure zone to a higher pressure zone. The use of lock hoppers inconjunction with pneumatic conveying is also well known in the art totransfer particles between vessels or zones that are maintained atdifferent pressures. First, a lock hopper transfers particles from theupper, low pressure source zone to a middle zone, and then to a lower,high pressure zone. A pneumatic conveying system then transfers theparticles from the high pressure zone to the destination zone. Althoughthe destination zone has a pressure less than that of the high pressurezone, the destination zone pressure may be greater than that of the lowpressure source. In the art, the term “lock hopper” has been used todesignate the combination of the upper, middle, and lower zones, and“lock hopper” has been used to designate only the middle zone.

In one example, the flow of particles from an upper vessel into themiddle zone and out of the middle zone into a lower zone is controlledby valves located in the conduits or transfer pipes that connect thezones. The valves may be double block-and-bleed ball valves. Thus, abatch of particles may be transferred to the middle zone through theupper valve or valves when the lower valve or valves are closed. Themiddle zone may then be isolated by closing the upper valve(s). Variousconduits may be connected to the isolated volume to introduce or removethe fluid phase, usually gas, or change the pressure inside the middlezone. For example, a regenerated catalyst may enter the vessel, bepurged with nitrogen to remove oxygen, and pressured with hydrogenbefore being transferred to the reactor which is at a higher pressurethan the regenerated catalyst. After catalyst exits the middle zone, themiddle zone can be purged with nitrogen to remove the hydrogen beforefilling again with catalyst.

U.S. Pat. No. 4,576,712 discloses a method and apparatus for maintaininga substantially continuous gas flow through particulate solids in twozones. The solids are moved from a low pressure zone to a high pressurezone by means of a valveless lock hopper system. Maintenance of gas flowwhile simultaneously transferring particles between zones isaccomplished without the use of moving equipment such as valves.

U.S. Pat. No. 4,872,969 discloses a method and apparatus for controllingthe transfer of particles between zones of different pressure usingparticle collection and particle transfer conduits. The solids are movedfrom a low pressure zone to a high pressure zone by means of a valvelesslock hopper system that vents all of the gas from the collection zonesthrough the particle collection conduits. The venting of gas isaccomplished by varying the size of the transfer conduits between zones.

As is known in the art, physical characteristics of the particles andbasic process information such as the operating pressure in the upperand lower zones and the acceptable range of gas flow rates are initialdesign information. Processes are designed from this basic informationand standard particle and gas engineering principles to routinelyprovide stable operating units. Surprisingly, it has been found that aparticular unit will operate predominantly in a stable manner butexperience sporadic upsets. These upsets involving a sudden surge ofparticles from one zone to another, which may reverse the particle flow,have been unpredictable with respect to which unit will be affected, andwhich particle transfer cycle will experience an upset in an affectedunit. These upsets occur despite conformance to the same design methods.Such upsets interrupt the consistent flow of particles and canphysically damage the particles as well as the equipment.

Consequently, there is desire to eliminate these sporadic upsets inorder to minimize damage to the equipment and particles and ensure theconsistent flow of particles. The consistent flow or transfer ofparticles involves a series of steps which are repeated in a cyclicmanner to transfer the particles in batches. Although it remainsunpredictable whether an upset will occur during any particular cycle inan apparatus, we have discovered that the upsets usually occur duringthe middle zone depressurization step or the middle zone empty step. Ourinvention provides an improved method and apparatus that eliminates allor many of these sporadic upsets without negatively impacting the vastmajority of operating units or cycles that do not experience upsets.

SUMMARY OF THE INVENTION

The invention is a method and apparatus for transferring particles froman upper zone through a middle zone to a lower zone where the zones areconnected by valveless conduits. The lower zone may have a higherpressure than the upper zone. A container within the lower zone is inparticle communication a valveless conduit. The transfer of particlesfrom the upper zone to the container within lower zone is controlled byvarying the pressure of the middle zone and the flow rates of gaspassing upwards through the valveless conduits. The container retains atleast a portion of the particles before they are passed through acontainer outlet to the volume of the lower zone outside the container.

In a broad embodiment, the invention is a method for transferringparticles from an upper zone, through a middle zone, to a lower zonecomprising: introducing a first gas stream into the lower zone;transferring particles downward from the upper zone to the middle zonethrough an upper valveless conduit, and transferring a second gas streamfrom the lower zone upward through a lower valveless conduit into themiddle zone; increasing the middle zone pressure; transferring particlesdownward from the middle zone, through the lower valveless conduit to acontainer within the lower zone, and transferring a third gas streamfrom the middle zone upward through the upper valveless conduit into theupper zone; decreasing the middle zone pressure; and transferringparticles from the container to a volume of the lower zone outside thecontainer.

In another broad embodiment, the invention is an apparatus comprising:an upper zone; a middle zone; a lower zone; a container located withinthe lower zone, the container comprising an inlet and an outlet; anupper valveless conduit extending from the upper zone to the middlezone; a lower valveless conduit extending from the middle zone to thelower zone, the lower valveless conduit providing particle communicationto the container; a gas inlet conduit providing fluid communication tothe lower zone; and a first gas conduit in fluid communication with themiddle zone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representative view depicting the zones of the apparatus indifferent vessels and an embodiment of the container in the lower zone.

FIG. 2 is a representative view depicting a particular arrangement ofgas conduits used in an embodiment of the invention.

FIG. 3 illustrates another embodiment of the gas conduits encompassed bythe invention and shows the zones of the apparatus within a singlevessel.

FIGS. 4A-4D and 5 illustrate various configurations of the lowervalveless conduit and container that are encompassed by the invention.

The Figures are intended to be illustrative of the invention and are notintended to limit the scope of the invention as set forth in the claims.The drawings are simplified diagrams showing exemplary embodimentshelpful for an understanding of the invention. Details well known in theart, such as cone deflectors, control valves, instrumentation, andsimilar hardware which are non-essential to an understanding of theinvention may not be shown.

DETAILED DESCRIPTION OF THE INVENTION

The invention may be used to transfer solid particulate matter from anupper zone, through a middle zone, to a lower zone where the lower zonepressure is greater than the upper zone pressure. The inventiontransfers particles without using moving equipment such as valves toblock the particle flow path. Generally, particles received in an upperzone are transferred through an upper valveless standpipe or transferconduit to a middle zone. A lower valveless standpipe or transferconduit is used to transfer the particles from the middle zone to acontainer located within a lower zone. Thus the zones, valvelessconduits, and container may be in particle communication and thevalveless conduits may provide particle communication.

The invention can be used within and/or between a variety of processunits to transfer particles, such as catalyst and adsorbents. The upperzone of the invention may receive particles from a separate process zoneand the lower zone may deliver the particles to another separate processzone. For example, an associated process unit may include a separatevessel that operates as a reaction zone which provides catalystparticles to the upper zone, and the lower zone may deliver catalyst toa separate process vessel such as a feed hopper of a pneumatic conveyingapparatus which in turn delivers the catalyst to the top of anotherreactor. In another embodiment, the invention may be arranged so thatthe upper zone and/or the lower zone are integrated with a process unitsuch that one or more process steps, or portions thereof, occurs withinthe upper and/or lower zones or the vessel(s) which contain the upperand/or lower zones. For example, the upper zone may be the lower portionof a reduction zone vessel or the entire reduction zone vessel of aprocess unit and/or the lower zone may be the upper portion of a surgevessel or the entire surge vessel of a process unit. The surge vessel inturn may introduce the particles into other zones of the same or adifferent process unit.

The invention may communicate with or the invention may comprise aportion of a process unit which provides for changing the fluid thatcontacts the particles. For example, the process unit may involvecontacting catalyst with a gas containing hydrocarbons and/or hydrogenin a reaction zone and removing carbon deposits from the catalyst usinga gas containing oxygen in a regeneration zone. As the catalyst istransferred between the reaction and regeneration zones, care must betaken to prevent mixing of the hydrocarbon/hydrogen atmosphere and theoxygen atmosphere. Examples of hydrocarbon conversion processes that mayemploy the invention include: alkylation, hydrorefining, hydrocracking,dehydrogenation, hydrogenation, hydrotreating, isomerization,dehydroisomerization, dehydrocyclization, and steam reforming. Onewidely practiced hydrocarbon conversion process that may employ theinvention is catalytic reforming using particles of catalyst. Exemplaryreaction and regeneration zones are disclosed in, e.g., U.S. Pat. No.5,858,210.

The upper, middle, and lower zones of the invention may be separatevessels or portions of separate vessels that are connected by valvelesstransfer conduits. In other embodiments, two or more of the upper,middle, and lower zones may be contained within a single vessel andseparated by dividers within the vessel. The upper, middle, and lowerzones of the invention may also provide one or more functions or processsteps of an associated process unit. In an embodiment, the upper,middle, and lower zones may be aligned sufficiently vertically to allowcatalyst to flow, at least in part, by gravity from at least one vesselat a higher elevation to at least one vessel at a lower elevation.

Flow of the particles into and out of the middle zone may be controlledby regulating the pressure of the middle zone, the flow rate of gasthrough each valveless particle transfer conduit, and the gas flow path.The same basic method steps may be accomplished by variousconfigurations of gas and particle conduits to introduce, vent, andchange the flow path of the gas used to control particle transfers. U.S.Pat. No. 4,576,712 and U.S. Pat. No. 4,872,969 disclose differentmethods and apparatus to control particle transfer and are herebyincorporated by reference in their entirety. The invention may use thesame basic method steps and is not limited to any particularconfiguration of the gas flow path and conduits. Existing configurationsand control schemes can be readily adapted to employ the invention.

The method of transferring particles from upper zone 10 to lower zone 30may be accomplished without blocking the particle transfer path withmoving equipment such as valves by repeating the following four stepcycle: 1) a fill or load step wherein particles are transferred from theupper zone to the middle zone; 2) a pressurization step wherein themiddle zone pressure is increased; 3) an empty step wherein particlesare transferred from the middle zone to the container within the lowerzone; and 4) a depressurization step wherein the middle zone pressure isdecreased. The steps may overlap. For example, transfer of particles maybegin while the middle zone pressure continues to increase or decreaseand the middle zone pressure may begin to increase or decrease whileparticles continue to transfer.

A single cycle results in the transfer of one batch of particles fromthe upper zone to the lower zone. The time required to complete onecycle, i.e. the cycle time, will depend on a variety of factorsincluding: the properties of the particles; the batch size, or amount ofparticles transferred per cycle; and the times needed to change thepressure of the middle zone. The invention is not limited by the cycletime. In an embodiment, the cycle time may be about 50 seconds. Inanother embodiment, the cycle time may be less than about 10 minutes,and the cycle time may be between about 2 minutes and about 4 minutes. Acontroller such as process control computers and programmablecontrollers may be used to regulate the cycle. The controller mayreceive various inputs, e.g. signals from particle level sensors,pressure gauges or indicators, differential pressure sensors, and timerssuch as for an individual step and/or the overall cycle. The controllermay also send signals for example to open, close, and adjust valves tocontrol the flow pattern and rate of various gas steams. Such acontroller and related signals are not shown in the figures as they arenot essential to the invention and are well known to the skilledartisan.

Broad embodiments of the invention will now be described with referenceto FIG. 1. In step 1 of the method, particles are transferred from upperzone 10 to middle zone 20 through upper valveless conduit 40. The upperand middle zones are at approximately the same pressure during step 1.Gas ascending through upper valveless conduit 40, if any, isinsufficient to retain the particles in conduit 40. During step 1, gasmay enter lower zone 30 through gas inlet conduit 11. Gas may also enterlower zone 30 from an associated process zone, not shown. Valve 12 mayregulate the quantity of gas flowing into lower zone 30; this flow ratemay be varied independently of the invention by means, not shown, forcontrolling the pressure of lower zone 30. The gas is selected to becompatible with the particles being transferred and may be the same gasas used in the associated process unit. Nitrogen, hydrogen, and air arenon-limiting examples of gas that may be used.

During step 1, gas flows upward from lower zone 30 through lowervalveless conduit 50 at a sufficient rate to retain the particles inconduit 50 thus causing middle zone 20 to fill with particles. Variousconfigurations of the gas flow path may be used. For example, a portionof the gas entering middle zone 20 from lower valveless conduit 50 mayflow through gas conduit 15 to upper zone 10 as shown in FIG. 2. Inother embodiments not illustrated, a portion of the gas may flow throughgas conduit 15 to another destination or simply be vented. In theembodiment illustrated in FIG. 3, which depicts the three zones of theapparatus in one vessel, upper valveless conduit 40 has a largerdiameter than lower valveless conduit 50 so that all gas entering middlezone 20 may flow through upper valveless conduit 40 at a flux which isinsufficient to retain the catalyst therein.

Upper 40 and/or lower 50 valveless particle transfer conduits may have arestriction, that is, a smaller cross-sectional area for particle flowthan the balance of the respective conduit. The cross-sectional areas ofthe restrictions if present and the balance of the conduit may be anyregular or irregular shape including a circle, oval, square, rectangle,and triangle. The cross-sectional area shape of a conduit may be thesame or it may differ over its length and may be the same or differentin the upper 40 and lower 50 valveless conduits. The cross-sectionalarea of a restriction and the balance of the conduit may have differentshapes or the same shape. The restriction may be located in a lowerportion of the conduit, that is, in the lower ⅓ of the respectiveconduit's height. The restrictions may be created in a wide variety ofways including crimping the conduit, using an insert, and forming theconduit with the restriction. Restrictions may be located proximate anoutlet in the lowermost end of the conduit. In an embodiment, theconduit, or a portion thereof is tapered toward the outlet to form therestriction at the outlet. The type, cross-sectional area shape, and/orlocation of restrictions in upper 40 and lower 50 valveless conduits maybe the same, or they may differ.

Step 1 ends when middle zone 20 is filled to its operating capacity withparticles. As shown in FIG. 1, upper valveless conduit 40 may extendinto middle zone 20 to define its operating capacity. That is, particlesstop flowing into the middle zone when particles in the middle zoneaccumulate to reach upper valveless conduit outlet 45. Thus, there maybe a continuous mass of particles from a lower portion of upper zone 10through upper valveless conduit 40, middle zone 20, and lower valvelessconduit 50. In another embodiment, the operating capacity of middle zone20 is predetermined and an optional upper level sensor, not show, isused to detect when particles rise to this preset level. In such anembodiment, particles need not reach upper valveless conduit outlet 45and upper valveless conduit 40 need not extend past the shell of middlezone 20. In other embodiments, the operating capacity of middle zone 20may be determined by a preset time interval. Use of an adjustable timinginterval or high level set point enables the size of each particle batchto be varied from cycle to cycle. The particle levels and/or timeincrements may be measured and a signal sent to a controller to initiatestep 2 when the middle zone has been filled. Thus, particles maycontinue to flow into middle zone 20 for a time after step 2 begins ifthe particles are below upper valveless conduit outlet 45 at the end ofstep 1. In other embodiments, the particle flow may be stopped at thispoint in the cycle and the apparatus may be held with middle zone 20filled to its operating capacity until it is desired to continue theparticle transfer cycle. This portion of the cycle may also be known asa separate hold or ready step. For example, in the embodiment of FIG. 2,valve 16 is closed to force all the gas upwards through both valvelessconduits thereby stopping particles from flowing out of both the upperand middle zones. Similarly, in the embodiment of FIG. 3, valve 14 canbe opened in addition to valve 12 to accomplish the same effect.

In step 2 of the cycle, the pressure within middle zone 20 is increased.The middle zone pressure may be increased to stop the transfer ofparticles from the upper zone. In an embodiment, the middle zonepressure is increased to equilibrate with the higher pressure in lowerzone 30. This may be accomplished by introducing gas into middle zone 20through gas conduit 13. Gas to gas conduit 13 may be supplied from avariety of sources including, but not limited to: gas inlet conduit 11,lower zone 30, and separate supply sources such as facility headers andother zones in the associated or other process units. In the embodimentillustrated in FIG. 2, valve 14 is opened and valve 16 is closed topressurize middle zone 20. In the embodiment shown in FIG. 3, middlezone 20 is pressurized by opening valve 14 and closing valve 12. Thereis no need to change the gas flow path as the cycle moves from step 2 tostep 3. However, as explained above there are numerous ways of routingthe gas flow path to control the desired particle movement. Thus, theinvention encompasses changing the gas flow path between and/or withinsteps 2 and 3 to equilibrate the middle and lower zone pressures andretain particles within upper valveless conduit 40.

Step 3 may be referred to as the empty step of the cycle. As thepressures in the middle and lower zones equalize, particles begin toflow from middle zone 20 through lower valveless conduit 50 to container60 which is located within lower zone 30. During step 3, gas flowsupward through upper valveless conduit 40 at a sufficient rate toprevent to prevent the transfer of particles from upper zone 10 intomiddle zone 20. The level of particles in middle zone 20 falls asparticles flow out of lower valveless conduit 50. A minimum particlelevel in middle zone 20 may be used to decrease the length requirementof lower valveless conduit 50. This may be accomplished in various wayssuch as using a preset time interval for the transfer, measuring theamount of particles that have entered lower zone 30, and measuring thelevel of particles remaining in middle zone 20. For example, low levelsensor 25 may detect the absence of particles at the low level set pointand send a signal to a controller to begin depressurizing or venting themiddle zone, step 4. Multiple inputs may be used to manage the particletransfer cycle steps. In an embodiment, the length of step 3 may becontrolled by a timer with low level sensor 25 being used initiate step4 early if the particles fall below the minimum level set point.

In step 4, the depressurization step, the pressure in middle zone 20 maybe decreased to equilibrate the middle and upper zone pressures. Inanother embodiment, the middle zone pressure may be decreased to stopthe transfer of particles from the middle zone. This may be accomplishedfor example by re-establishing the gas flows that were used in step 1.Thus, in the embodiment of FIG. 2 valve 14 may be closed and valve 16opened so that the gas flux upward in lower valveless conduit 50 issufficient to retain particles therein while sufficient gas flowsthrough gas conduit 15 to equalize the pressure between the upper andmiddle zones. In other embodiments not illustrated, a portion of the gasmay flow through gas conduit 15 to another destination or simply bevented. In the embodiment illustrated in FIG. 3, valve 14 is closed andvalve 12 is opened to re-establish the gas flow path of step 1 of thatembodiment.

When the pressure of middle zone 20 is decreased in step 4 toequilibrate with upper zone 10 and increased in step 2 to equilibratewith lower zone 30 it is understood that the pressures in the two zones,superior and inferior, being equilibrated may or may not be the same.For example, pressure differences may exist, if there is some gas flowbetween the two equilibrated zones, or if they are being controlledindependently. Also, there is no requirement that the inferior zone beat the same or lower pressure than the superior zone of the two zonesbeing equilibrated. That is, particles may transfer from either superiorzone to the respective inferior zone even though the pressure of theinferior zone is higher than the pressure of the superior zone. The gasflow paths described for the embodiments of FIGS. 2 and 3 show that theinvention may provide for the continuous flow of gas to each of theupper, middle, and lower zones throughout a cycle. Further, theembodiment of FIG. 2 provides an uninterrupted flow of gas from thelower zone through the middle zone and into the upper zone throughoutthe cycle. In other embodiments not illustrated, various gas conduitsmay be used to control the middle zone pressure and the gas flow ratesthrough the upper and lower valveless particle transfer conduits toregulate the particle movement as herein described.

It is understood that the step numbers used herein are arbitrary and atransfer cycle may be considered to begin with any step and each step isemployed at least once during a cycle. The invention encompasses variousorders of the steps and some steps may be repeated in the course oftransferring a single batch of particles from the upper zone to thelower zone. For example, the transfer of particles in steps 1 and/or 3may be interrupted by employing steps 2 and 4 multiple times during atransfer cycle. Thus, in an embodiment, the order of steps may be1—transfer particles from the upper zone to the middle zone; 2—increasethe middle zone pressure to stop the transfer of particles; 4—decreasethe middle zone pressure to equilibrate the middle and upper zonepressures; 1—transfer particles from the upper zone to the middle zone;2—increase the middle zone pressure to equilibrate the middle and lowerzone pressures; 3—transfer particles from the middle zone to thecontainer within the lower zone; and 4—decrease the middle zone pressureto equilibrate the middle and upper zone pressures. In anotherembodiment the order of steps may be 1, 2, 4, 1, 2, 3, 4, 2, 3, and 4.Other steps such as purging the middle zone may be included in atransfer cycle.

Returning to the discussion of step 3. Container 60 is located withinlower zone 30 to receive particles emerging from lower valveless conduit50. Container 60 may be spaced apart from the inside surface of thelower zone and secured via one or more support elements 67. For example,the container may be suspended such as by wires or rods 67′ in FIG. 2;fastened to or supported by relatively horizontal rails or beams 67″ inFIG. 3; or located on a stand secured to a lower portion of the zone.Such supports which are known in the art may be used in any combinationto locate the container 60 relative to the lower valveless conduit 50 asdescribed herein. These support elements may in turn be secured to anyinside surface of the lower zone or any other internal structures withinthe lower zone including lower valveless conduit 50. The container andsupport elements may be of the same or different material ofconstruction suitable for the process conditions. In an embodiment, thesupport is of the same material of construction as that of the lowerzone inside surface.

In the embodiments of FIGS. 1-3, container 60 is located below andspaced vertically apart from outlet 55 of the lower valveless conduit50. Thus, particles may emerge or be discharged from outlet 55 of lowervalveless conduit 50 and then pass to container 60 through inlet 62. Thecontainer is an open top cylindrical form with a solid bottom plate andoutlet 65 located in a lower portion of the sidewall. Particles passfrom container 60 through outlet 65 to the volume of lower zone 30outside the container. In an embodiment, particles passing fromcontainer 60 through outlet 65 fall freely to a lower portion of lowerzone 30. That is, the container may be located above and spaced apartfrom accumulated particles in lower zone 30. Lower valveless conduit 50preferably extends into lower zone 30 as shown in FIG. 1, though thisextension into lower zone 30 is not required.

FIGS. 4A-4D illustrate a few non-limiting configurations of the lowervalveless transfer conduit 50 and the container 60 which are encompassedby the invention. Although the configurations differ, the same referencenumerals are used to identify the corresponding elements in each Figure.The support element(s) are not illustrated in these views as they arenot necessary for an understanding of the configurations. In anembodiment, the surfaces of the container are imperforate. In anotherembodiment, all or a portion of the surfaces may have uniform ornon-uniform perforations. As used herein, “perforations” includes holes,gaps, slots, other openings, and combinations thereof which aresufficiently small to retain the particles while allowing gas to passthrough the surface.

In the embodiment of FIG. 4A, container 60 has a square form the bottomsurface of which is tapered towards outlet 65 located the lowermostportion of the container. Inlet 62 may be in the uppermost surface ofthe container, and the inlet permits the entry of particles where lowervalveless conduit 50 extends through the inlet to discharge particlesdirectly into the volume of the container. As shown in FIG. 4B, lowervalveless conduit 50 need not extend into lower zone 30 and more thanone such conduit may be used. Container inlet 62 may comprise multipleopenings in the uppermost surface 63 of the container which ispositioned to receive the particles. Container outlet 65 may comprisemultiple openings in the lowermost surface of the container. There is norequirement that the number of conduits, inlet openings, and outletopenings be the same. FIG. 4C shows container 60 may be in the form of afunnel. The container surface or sidewall may also be a support elementfor the container by being extended and attached to the inside surfaceof the lower zone. The uppermost surface 63 of the container may be thetop edge of a surface wall or sidewall of the container. As illustrated,the lower valveless conduit 50 may extend to the inlet of container 60such that the lower valveless conduit and the container are not spacedvertically apart. As shown, a container may be asymmetrical. FIG. 4Dshows that container inlet 62 is not required to be in the uppermostsurface of the container. This embodiment also shows that the lowervalveless conduit 50 need not be strictly vertical, but may be angledrelative to true vertical. Also, a conduit may be tapered along itsentire length or a portion thereof towards outlet 55. These non-verticaland tapering embodiments may also be used in upper conduit 40. Lowerconduit 50 may be connected to container inlet 62. These conduitconfigurations may be used independently. When outlet 65 comprisesmultiple openings, the openings may be configured differently, e.g. bein different locations and have different sizes and shapes size. Thecontainer outlet has a cross-sectional area equal to the sum of thecross-sectional areas of each outlet opening. The cross-sectional areaof the container inlet is determined in the same manner. Likewise,multiple inlet openings and conduits may be configured differently.

In an embodiment, container 60 has a top surface which is above animaginary, horizontal plane that bisects the height of the container anda bottom surface which is below this imaginary plane. The container'sheight is the vertical distance between the uppermost and lowermostpoints of the container's surfaces. Container inlet 62 may be located inthe top surface of the container. In an embodiment, the inlet is locatedin the uppermost portion of the top surface, i.e., the uppermost surfaceof the container. Container outlet 65 may be located in the bottomsurface of the container. Particles are discharged or transferred fromthe container through the outlet into the volume of the lower zoneoutside the container. In an embodiment, the container outlet is locatedin the lowermost portion of the bottom surface, i.e., the lowermostsurface of the container. When a container outlet is located in aparticular surface, it is only necessary for one opening of the outletto be in that surface. Other outlet openings, if any, may be located inthe same surface or elsewhere. The same is true for the container inlet.

Container 60 may be fabricated in any shape sufficient to retain atleast a portion of the particles discharged by lower valveless conduit50 during step 3. Particles accumulate within container 60 during step 3and reach a level to contact the lower valveless transfer conduit outlet55. That is, container 60 and lower valveless conduit 50 are configuredto form a continuous mass of particles between middle zone 20 andcontainer 60 through lower valveless conduit 50 during a portion of theparticle transfer cycle. The particle transfer rate from the middle zonemay vary during step 3. For example, the continuous mass of particlesmay be formed during step 3 when the particle transfer rate from conduit50 into the container is greater than the particle transfer rate fromthe container through outlet 65 to the lower zone volume outside thecontainer. The particles may then continue to transfer from the middlezone to the container moving as a continuous mass, limited by theparticle transfer rate out of the container. The level of particlesretained by the container may then fall below conduit outlet 55 as theparticle transfer rate from conduit 50 decreases. Similar to thetransition to step 2 pressurization, particle transfer to the containermay continue during a portion of step 4, depressurization. Also,particle transfer from the container to the volume of the lower zoneoutside the container may continue during at least a portion of step 4.

Container outlet 65 may be sized and configured to control the particletransfer rate from container 60 to the volume of lower zone 30 outsidethe container. For example, outlet 65 may comprise multiple openings ofvarious shapes and cross-sectional areas arranged at differentlocations, such as various heights in the container surface. In anembodiment, the cross-sectional area, A2, of container outlet 65 is lessthan the minimum cross-sectional area of the lower valveless conduit 50.The particle transfer rate from the container through outlet 65 may beless than the particle transfer rate from the lower valveless conduit tothe container. As shown in FIG. 5, the cross-sectional area, A2, ofoutlet 65, being the sum of the cross-sectional areas of the outletopenings, may be less than the cross-sectional area, A1, of lowervalveless conduit outlet 55. In an embodiment, container inlet 62 has across-sectional area, A3, which is greater than the cross-sectionalarea, A1, of lower valveless conduit outlet 55. FIG. 5 illustrates thattapering of a valveless conduit towards the outlet does not require anextensive distance along the conduit.

The size of the container may be related to the batch size of particlestransferred from the middle zone during a cycle of the method, i.e. themiddle zone operating capacity less the volume of particles remaining inthe middle zone when step 4 is initiated. The container may be smallerthan the volume of a single batch of particles. For example, particlesmay flow out of the container as it is being filled and particles mayform a mound above the container. The container may be larger than theparticle batch volume such as when the lower valveless conduit extendsinto the container. As the particle batch size may vary, the minimumcontainer volume may be related to the minimum particle batch size. Theupper limit of the container volume is constrained by the design of thelower zone including the lower zone volume and the volume of particlesto be maintained within the lower zone. In an embodiment, the volume ofthe container is at least about 30% of the minimum particle batchvolume. The container volume may be at least about 60% of the minimumparticle batch volume, and in another embodiment, the container volumeis at least about the same as the minimum particle batch volume.

By regulating the particle transfer rates to and from container 60, theformation and continued existence of the continuous mass of particlesfrom the middle zone to the container may be controlled. In anembodiment, this continuous mass of particles may exist for a portion ofstep 3. In another embodiment, the continuous mass of particles mayexist for a portion of step 4; and the level of particles retained bycontainer 60 may fall below the level of conduit outlet 55 before thebeginning of step 1. Thus, particles may transfer from the container tothe volume of lower zone 30 outside the container during step 4. In yetanother embodiment, container 60 and outlet 65 are configured toessentially empty the container of particles before the subsequent step3 begins such as by locating outlet 65 in the lowermost surface ofcontainer 60. That is, particles may occupy less than about 10% of thecontainer volume when step 3 begins; and in an embodiment, particlesoccupy less than about 5% of the container volume at this time.Particles may occupy less than about 3% of the container volume whenstep 3 begins.

In an embodiment, particles may form a mound which contacts lowervalveless conduit outlet 55. The mound may be wholly within container 60or it may extend above container inlet 62 to reach conduit outlet 55.That is, the volume of particles retained by the container may begreater than the volume of the container. If particles mound above thecontainer inlet, particles may fall or slide down the mound into thevolume of the lower zone outside the container without passing throughthe container volume. Lower valveless conduit 50 provides particlecommunication to container 60; and lower valveless conduit 50 andcontainer 60 may be in particle communication even if the lowervalveless conduit and container are not connected. Container 60 andlower valveless conduit 50 may be spaced apart by a distance D. In anembodiment, the vertical distance, D, separating container inlet 62 andlower valveless conduit outlet 55 is less than about 1.15*R*tan θ, whereR is the effective radius of the cross-sectional area, A3, of thecontainer inlet 62 and θ is the angle of repose of the particles. Inanother embodiment, D may be less about 1.07*R*tan θ; and D may be lessthan about R*tan θ. The effective radius of the cross-sectional area ofthe container inlet is the radius of a circle having the samecross-sectional area of the container inlet. The angle of repose of theparticles is a well known property of particles that is determined bydepositing the particles on a horizontal surface with negligiblevelocity to form a pile. The angle formed between the slope of the pileand the horizontal surface is the angle of repose. See Andrew W. Jenike,Storage and Flow of Solids, Bulletin No. 123 of the Utah EngineeringExperiment Station Sixth Printing (revised), March, 1970, University ofUtah.

During the particle transfer cycle, the inventory in upper zone 10 maybe continuously and/or intermittently replenished with particles such asfrom an associated or integrated process zone and/or as added from afresh particle feed hopper. Likewise, particles delivered to lower zone30 may be withdrawn from or pass out of the lower zone continuouslyand/or intermittently. It is preferred that an inventory or surge volumeof particles be maintained in both the upper and lower zones throughoutthe particle transfer cycle. As previously described, upper zone 10 mayalso provide one or more functions of an associated or integratedprocess unit including regeneration zones. Non-limiting examplesinclude: a particle feed hopper, a reaction zone, an atmosphere purgezone, another catalyst transfer zone, a reduction zone, and anelutriation zone. The internal pressure of upper zone 10 may beindependently controlled by means well known in the art. For example,upper zone 10 may be in fluid communication with a process zone so thatthe upper zone pressure depends upon and varies with the pressure inthat process zone. The upper zone pressure is not critical and may beatmospheric, sub-atmospheric, or super atmospheric.

Lower zone 30 may be a holding vessel, or surge zone from which theparticles are transferred by other means such as pneumatic conveying. Inother embodiments, lower zone 30 may provide one or more functions of anassociated or integrated process unit including regeneration zones.Non-limiting examples include: a particle feed hopper, a reaction zone,an atmosphere purge zone, another catalyst transfer zone, a reductionzone, and an elutriation zone. The internal pressure of lower zone 30may be independently controlled by means well known in the art. Forexample, lower zone 30 may be in fluid communication with a process zoneso that the lower zone pressure depends upon and varies with thepressure in that process zone. In an embodiment, the upper zone pressuremay be higher than the lower zone pressure for a portion of the transfercycle. In another embodiment, lower zone 30 may be maintained at ahigher pressure than upper zone 10. For example, upper zone 10 may bemaintained at a nominal pressure of 34 kPa (g) and permitted to varywithin a range from about 14 to about 55 kPa (g) while the nominalpressure of lower zone 30 may be 241 kPa (g) within a range from about207 to about 276 kPa (g). In another embodiment, upper zone 10 may bemaintained at a nominal pressure of 241 kPa (g) and permitted to varywithin a range from about 172 to about 310 kPa (g) while the pressure oflower zone 30 may be within a range from about 345 to about 2068 kPa(g). Thus, the differential pressure between the lower zone 30 and upperzone 10 might range from about 35 to about 1896 kPa. However, thisinvention may be used when the pressure differential between zones is aslittle as about 0.7 kPa and in excess of 2000 kPa. Middle zone 20 servesas an intermediate zone, and its nominal pressure is adjusted toregulate the flow of the particles.

The apparatus of the invention may be used as a solids flow controldevice for an entire process, since the flow rate of particles from theupper zone to the lower zone can be varied, as discussed above. Theupper, middle, and lower zones may contain other non illustratedapparatus known in the art such as baffles, screens, and deflector coneswhich may be used to facilitate particle flow and/or direct theparticles or the gas through a zone in a desired manner. The componentsof the present invention may be fabricated from suitable materials ofconstruction, such as metals, plastics, polymers, and composites knownto the skilled artisan for compatibility with the particles, andoperating conditions, e.g. gas, temperature, and pressure. The size,shape, and density of the particles is only limited by the size of theequipment and the type and flow rates of the gas or gases used. In anembodiment, the particles are spheroidal and have a diameter from about0.7 mm to about 6.5 mm. In another embodiment, the particles have adiameter from about 1.5 mm to about 3 mm. The particles may be catalystsan example of which is disclosed in U.S. Pat. No. 6,034,018.

As previously noted, particle transfer apparatus of the prior art may beadapted to incorporate the invention. Likewise, standard engineeringprinciples especially those related to the flow of solids and gases andknown design methods may be used in this invention. In addition to theteachings herein, the design considerations and methodology described inU.S. Pat. No. 4,576,712 and U.S. Pat. No. 4,872,969 may be used topractice this invention. For example, the pressure in the upper andlower zones, the minimum and maximum gas flow rates upwards through thezones and the valveless conduits, and the required particle transferrate are design factors that are often fixed by the associated processunit. The length of the particle column inside the valveless conduit,the height of particles in the zone above the valveless conduit, and thediameter of the conduit may be balanced so that changing the pressuresand gas flow paths as described herein controls whether particles willflow down through or be retained within the conduit. The design methodincludes limiting the gas flow rates and pressure differentials to avoidfluidizing particles within the zones and to prevent particles frombeing suddenly forced up or down the valveless conduits. It is wellknown to those skilled in the art in design of solids flow systems toconduct experiments to determine flow characteristics of the particularsolid involved.

Thus, it is known that the internal pressures of the upper and lowerzones, the minimum and maximum gas flow rates, the identities of the gasand the particles, and the required range of particle transfer rates,may be used to determine various parameters of the invention. Theseparameters include: the normal minimum and maximum volumes occupied bythe particles in the zones, the particle heights required in the zonesabove the transfer conduits, the diameter of the transfer conduits, andthe lengths of the transfer conduits. These and other parameters such asthe gas conduit size and arrangement may characterize a particularembodiment encompassed by the invention.

1. A method for transferring particles from an upper zone, through amiddle zone, to a lower zone comprising: (a) introducing a first gasstream into the lower zone; (b) transferring particles downward from theupper zone to the middle zone through an upper valveless conduit, andtransferring gas from the lower zone upward through a lower valvelessconduit into the middle zone; (c) increasing the middle zone pressure;(d) transferring particles downward from the middle zone, through thelower valveless conduit to a container within the lower zone, andtransferring gas from the middle zone upward through the upper valvelessconduit into the upper zone; (e) decreasing the middle zone pressure;and (f) transferring particles from the container to a volume of thelower zone outside the container.
 2. The method of claim 1 furthercomprising maintaining an inventory of particles in the upper zone, andmaintaining an inventory of particles in the lower zone.
 3. The methodof claim 1 further comprising sensing the level of particles in themiddle zone, and transmitting a signal to initiate step (e).
 4. Themethod of claim 1 wherein at least portions of steps (e) and (f) aresimultaneous.
 5. The method of claim 1 wherein particles transferred tothe container are discharged from an outlet of the lower valvelessconduit and then pass through an inlet of the container.
 6. The methodof claim 1 wherein particles transferred to the container are dischargedfrom an outlet of the lower valveless conduit, the outlet being locatedwithin the lower zone.
 7. The method of claim 1 wherein particlestransferred to the container are discharged from an outlet of the lowervalveless conduit, the outlet being located within the container.
 8. Themethod of claim 1 wherein the upper zone is at a first pressure, thelower zone is at a second pressure, and the second pressure is greaterthan the first pressure.
 9. The method of claim 1 wherein the pressurein the middle zone is greater than a pressure in the upper zone duringat least a portion of step (c).
 10. The method of claim 1 furthercomprising during step (d) forming a continuous mass of particlescomprising particles in the middle zone, particles in the lowervalveless conduit, and particles in the container.
 11. The method ofclaim 10 wherein the continuous mass of particles exists when step (e)is initiated.
 12. The method of claim 1 wherein particles aretransferred from the middle zone, through the lower valveless conduit,to the container at a first rate, and particles are transferred from thecontainer to the volume of the lower zone outside the container at asecond rate wherein the first rate is greater than the second rate. 13.The method of claim 1 further comprising introducing a second gas streamto the middle zone to increase the middle zone pressure in step (c) andventing gas from the middle zone to the upper zone through the uppervalveless conduit in step (e).
 14. The method of claim 1 furthercomprising transferring at least a portion of gas from the lower zone tothe middle zone through a first gas conduit to increase the middle zonepressure in step (c), and venting gas from the middle zone through asecond gas conduit in step (e).
 15. The method of claim 14 wherein themiddle zone is vented through the second gas conduit to the upper zonein step (e).
 16. The method of claim 1 wherein during step (c) themiddle zone pressure is equilibrated with the lower zone pressure, andduring step (e) the middle zone pressure is equilibrated with the upperzone pressure.
 17. A method for transferring particles from an upperzone, through a middle zone, to a lower zone comprising: (a) introducinga first gas stream into the lower zone; (b) transferring particlesdownward from the upper zone to the middle zone through an uppervalveless conduit, transferring gas from the middle zone to the upperzone through the upper valveless conduit, and transferring gas from thelower zone upward through a lower valveless conduit into the middlezone; (c) introducing a second gas stream to the middle zone to increasethe middle zone pressure; (d) transferring particles downward from themiddle zone, through the lower valveless conduit, to a container locatedin the lower zone, and transferring gas from the middle zone upwardthrough the upper valveless conduit into the upper zone; (e) venting themiddle zone to the upper zone through the upper valveless conduit todecrease the middle zone pressure; and (f) transferring particles fromthe container to a volume of the lower zone below the container.
 18. Themethod of claim 17 further comprising during step (d) forming acontinuous mass of particles comprising particles in the middle zone,particles in the lower valveless conduit, and particles in thecontainer.
 19. A method for transferring particles from an upper zone,through an middle zone, to a lower zone comprising: (a) introducing afirst gas stream into the lower zone; (b) transferring particlesdownward from the upper zone to the middle zone through an uppervalveless conduit, and transferring gas from the lower zone upwardthrough a lower valveless conduit into the middle zone; (c) transferringat least a portion of the gas from the lower zone to the middle zonethrough a first gas conduit to increase the middle zone pressure; (d)transferring particles downward from the middle zone through the lowervalveless conduit to a container located in the lower zone, andtransferring gas from the middle zone upward through the upper valvelessconduit into the upper zone; (e) venting the middle zone through asecond gas conduit to decrease the middle zone pressure; and (f)transferring particles from the container to a volume of the lower zonebelow the container.
 20. The method of claim 19 wherein the middle zoneis vented through the second gas conduit to the upper zone.
 21. Themethod of claim 19 further comprising during step (d) forming acontinuous mass of particles comprising particles in the middle zone,particles in the lower valveless conduit, and particles in thecontainer.